A partial band-whole band energy discriminator as disclosed in copending U.S. patent application Ser. No. 240,977 filed concurrently herewith is employed to inhibit updating of an adaptive filter employed in an echo canceler during intervals that partial band energy is detected in a received signal. The received energy is discriminated as being partial band or whole band and the echo canceler is enabled to adjust an echo estimate being generated only when whole band energy is being received. That is to say, the echo estimate is enabled to be adjusted during intervals that significant far end energy is being received and the energy is determined not to be partial band and, therefore, is defined as being whole band. The apparatus employed to discriminate between partial band and whole band energy as disclosed in the application Ser. No. 240,977 is sophisticated and presently would require a substantial area of an integrated chip, if not several chips.
In another energy discriminator as disclosed in U.S. patent application Ser. No. 240,979 filed concurrently herewith whole band energy and partial band energy in a received far end signal are distinguished by comparing a signal representative of an average value of the received signal to a signal representative of a modified magnitude value of the received signal. When the modified magnitude of the received signal exceeds the average value, the received signal includes whole band energy and updating of the echo estimate is enabled for at least a predetermined interval. When the modified magnitude does not exceed the average, the received signal includes only partial band energy and updating of the echo estimate is inhibited.
This arrangement uses an initial interval wait timer to protect against falsely indicating detection of whole band energy until the circuit stabilizes and a socalled hangover timer to generate a control signal for enabling the echo canceler updating for at least a predetermined interval. It has been determined that use of such techniques somewhat limits over all performance in distinguishing between whole band and partial band energy. Indeed, once the hangover timer times-out the control signal changes state and updating of the echo estimate is immediately inhibited.